Anode structure



Aug. 7, 1962 H. E. KREFFT 3,

ANODE STRUCTURE Filed Sept. 17, 1959 3 Sheets-Sheet 1 INVENTOR. H. EKEEFF' T Aug. 7, 1962 H. E. KREFFT 3,048,727

ANODE STRUCTURE Filed Sept. 1' 1959 5 Sheets-Sheet 2 INVENTOR. M E.KEEFFT F76. 4 I WW)- A TTOENEY H. E. KREFFT ANODE STRUCTURE Aug. 7, 1962Filed Sept. 17, 1959 5 Sheets-Sheet 3 32 3 i I 2TH 35 f V g INVENTOR.F/G 6 H. E. KEEFl-"T BY z z A Tro mvsv United States Patent 3,048,727ANODE STRUCTURE Hermann E. Krelft, East Orange, N.J., assignmto KutheLaboratories, Incorporated Filed Sept. 17, 1959, Ser. No. 840,772 9Claims. (Cl. 313-39) The invention relates to an anode structure forelectrical discharge tubes, such as rectifier or switch tubes. Moreparticularly, it relates to hydrogen filled thyratron tubes which areprovided with a ceramic envelope, and in which the anode forms part ofthe envelope wall.

In hydrogen thyratrons, which are switch tubes operated with currentpulses of extremely high magnitude and short duration, the anode is,under certain conditions, for instance, low operating pressure or highpulse repetition rates, heated to a very high temperature which may leadto the destruction of the tube. In order to avoid such overheating, theanode is made from a material having high thermal conductivity, likecopper, where feasible, and it is directly exposed to the atmosphere bymaking it a part of the tube envelope. However, those parts of the anodewhich are struck by the discharge have to be made from a more refractorymaterial like molybdenum or tungsten which are poor conductors of heat.In order to provide good thermal contact, these materials have to beconnected to the copper components of the structure by brazing which isdifflcult to carry out, as molybdenum or tungsten have low thermalexpansion, while that of copper is three to four times as high. Brazingof such different materials naturally results in a considerabledeformation of the brazed assembly which is highly undesirable formechanical and electrical reasons.

In view of these imperfections, it is one object of the invention toprovide an anode structure which is not deformed in a harmful manner;another object is to provide an anode structure which will not overheatunder a high load; still another object is to provide a structure whichpermits exhausting the tube through the anode.

These objects are attained by providing an anode plate with a massivesupport structure consisting of a slotted ring behind those portions ofthe plate receiving the electrical discharge and forming paths forconducting heat rapidly away from the plate.

The above-mentioned and other features and objects of this inventionwill become apparent by reference to the following description taken inconjunction with the accompanying drawings, in which:

FIG. 1 is an exploded view of the anode structure;

FIG. 2 is a bottom view of the structure with the anode plate partlyremoved;

FIG. 3 is a. partly sectional side view of the same structure;

FIG. 4 is an enlarged sectional view illustrating the brazed connectionswithin the anode structure;

FIG. 5 shows the anode structure as a part of a ceramic thyratron tube;and

FIG. 6 illustrate a modification of the anode structure provided with anexhaust tubulation.

As shown in FIGURES 1, 2 and 3 which illustrate a preferred embodimentof the invention, the novel anode structure consists of a round flatplate 1, a compact cylindrical support structure 2 which will be calledthe anode block, and a thin walled flanged cup 3 to which the anodeblock is firmly connected. The plate 1 is made from a highly refractorymetal as, for example, molybdenum or tungsten, which metals possess arelatively low thermal expansion. It is this part of the anode structurewhich is exposed to the major portion of the discharge resulting inlarge amounts of heat being generated in this region during operation ofthe tube. This thermal energy must be removed quickly from the platewhich otherwise would become incandescent and the tube inoperable. Heatfrom the plate is efliciently carried away by the anode block 2 which ismade from pure high conductivity copper and has a relatively large mass.Connection between these two parts is made by brazing. The anode block 2is positioned within the flanged cup 3, which is preferably made fromhigh conductivity coper, and is brazed to the inside of the cup, asshown in FIG. 3. This structure is sealed to one end of a ceramic tubeenvelope so that a fraction of the heat absorbed by the cup will beconducted to the ceramic envelope by means of a flange 4, which formspart of the cup 3. In this position the upper side 5 of the anode blockis exposed to the atmosphere and forms part of the tube wall. Electricalconnection to the anode is made by means of a tapped hole 6 situated ina thickened portion of the' upper side 5 of the anode block.

Brazing of the anode plate 1 to the block 2 presents a serious problemwhich stems from the considerable difference in thermal expansionexisting between molybdenum or tungsten, and copper, which has a thermalexpansion of 10- as compared to 55 10-' and 44x10- respectively, for theother two metals. When brazed together, these metals form a bimetallicsystem which tends to bow or deform in some uncontrolled way whencooling. This results in a warped anode which would make alignment andspacing within the tube, and sealing to the ceramic envelope, verydifficult if not impossible. This difiiculty is overcome in accordancewith the invention, by slotting the thick-walled cylindrical part of theanode block which, in this way, is divided into numerous equal segments7 by a plurality of radial slots 8, as shown in FIGURES 2 and 3 in moredetail. These segments as a whole provide more flexibility than a solidcylinder as each may more easily yield to radial or tangential forcespresent during the cooling period after brazing, or during anysubsequent change in temperature. Radial flexibility is furtherincreased by an undercut 9 in each segment. Thermal conductivity andremoval of heat from the anode plate is not appreciably affected byslotting of the block, as the slots can be made very narrow, forinstance, of an inch. An anode structure utilizing a slotted block stillsuffers a small deformation after brazing at about 1000 C. andsubsequent cooling to room temperature; but the deformation now consistsof a slight bow which will be entirely symmetrical. A molybdenum anodeplate of 2 /2 inches diameter and A of an inch thickness, for example,has a uniform bow corresponding to ten one thousandth of an inchdeviation at the center from a plane passing through the periphery.

The brazed connections between the three component parts constitutingthe anode structure are shown in more detail in FIG. 4. A particularlysafe method for producing a brazed connection of great mechanicalstrength between anode plate 1 and anode block 2 is provided by settingthe segments 7 of the anode block in a flat groove about 6 of an inchdeep machined into the surface of the anode plate. The bra-zedconnection is made between the plane faces of the segments 7 and thebottom and side Walls of the groove. As brazing material, an alloycomposed of 82% gold and 18% nickel is used, which, as a washer 36, isplaced in the groove 10' of anode plate 1 between the two parts when thestructure is being assembled. After brazing, the faces are firmlyconnected to each other and fillets 11 are formed on both sides andbetween the segments which provide additional strength. At the same timeas this operation is carried out, the anode block 2 is brazed to theinside of the flanged cup 3, as illustrated by FIG. 4. In order toposition the anode block within the cup correctly, so that a smallclearance 35 of about A.; of an inch is maintained between the plate andthe plane end of the cup 3, a step 12 is provided in the inner cup wallwhich supports the flat bottom part 13 of the anode block. Brazingmaterial is provided by a gold-copper alloy brazing ring 37 which isplaced on the ring shaped end 14 of the anode block in close contactwith the cup wall when the anode structure is assembled for brazing. Asa result of the brazing, the bottom part 13 is joined over its wholecircumference to the inner wall of the cup, and a fillet 15 of brazingmaterial is formed.

The anode structure, as described, is sealed to the ceramic envelope ofa thyratron tube in a manner illustrated in FIG. 5. The seal is madebetween the metallized faces of ceramic body ring 16 and ceramic endring 17, and the flange 4 of the anode cup. Silver-copper alloy is usedas brazing material. In tubes of this kind, the small clearance 18between the anode cup and the inner wall of the envelope is verycritical and must be kept within a few thousandths of an inch in orderto avoid uncontrolled electrical breakdown between the anode and thegrid 19 or the cathode 20. An anode structure which is not distorted andwhich permits good alignment with the envelope wall is, therefore,indispensable. The entire tube envelope is formed by this sectioncontaining the anode, a second body ring 21, and a cup shaped base 22which is sealed, by means of a flange 23, to the end of body ring 21 inthe same manner as the anode to body ring 16. In a similar way, a flange24 which forms part of a grid structure 19, is sealed between the otherfaces of body rings 16 and 21. The base is provided with insulatedlead-in terminals 25, 26 through which a heating current is supplied tothe indirectly heated cathode 20, and it further has an exhausttabulation 27, shown as it appears after tipping oif the tube.

During operation, pulsed gas discharge currents having high peak valuespass from the cathode to the anode plate 1. This discharge is made tooperate through a tortuous passageway imposed by the grid structure 19which, in the case illustrated by FIG. 5, consists of sixteen shortradial slots 28 near the periphery and a baffle 29 which has one centralaperture only. Additional baffling is provided by a disc 30 and a shield31 which are interposed between the cathode and the grid structure.Thus, the discharge, after leaving the grid on its way to the anode, iscomposed of sixteen narrow beams which strike the anode plate in sixteenwell defined spots. As heat is generated on the plate at these spotsonly it is obvious that heat conductive backing of the anode block isnecessary in these areas, and that the other areas may be left withoutsuch backing. In the example described in this specification, theposition of the segments which form part of the anode block is adaptedto the pattern of the discharge beams. For other beam patterns, adifferent arrangement of the segments is desirable and even necessary,since, as a general rule, the segments should always be adjacent thepoints where the discharge hits the anode plate, so that heat has totravel a mini- 4 mum distance through the plate and is quickly passed tothe block 2 In a modification of the anode structure described, theanode block has a central bore 32 to which is connected an exhausttabulation 33, as shown in FIGURE 6. Exhaust of the tube through theanode is desirable for a number of reasons. However, an exhaust channelcannot be used in conventional anodes, as so-called long path conditionsfor the discharge are produced which cause electrical breakdown betweenthe anode and other electrodes. These conditions do not exist in ananode structure constructed according to the invention, as the aperture34 of the exhaust channel is not directly exposed to the discharge.Connection from this channel to the inside of the tube is made throughthe narrow slots 8 in the anode block, and through the small clearance35 of approximately of an inch which is provided between the cup 3 andanode plate 1. High exhaust speed is obtained in these passageways owingto the large number of slots and the large circumference of theplate-tocup clearance. This narrow gap does not interfere with thedischarge.

While I have described above the principle of my invention in connectionwith specific apparatus, it is to be clearly understood that thisdescription is made only by way of example and not as a limitation tothe scope of my invention as set forth in the objects thereof and in theaccompanying claims.

What is claimed is:

1. An electron discharge device comprising an envelope, a cathode, andan anode plate, means for mounting said cathode and said anode plate inspaced relation, and heat conducting means in contact with said anodeplate for conducting heat away from said plate, said heat conductingmeans comprising a plurality of symmetrically spaced blocks on theopposite side of said plate from said cathode for preventing deformationdue to thermal distortion of said heat conducting means.

2. An electron discharge device comprising an envelope, a cathode, aconductive gas within said envelope, an anode plate, mean for mountingsaid cathode and said anode plate in spaced relation, means fordirecting discharge from said cathode to symmetrically spaced portionsof said plate, and heat conducting means in contact with said anodeplate for conducting heat away from said plate, said heat conductingmeans comprising a plurality of blocks on the opposite side of saidplate from said cathode and spaced in alignment with the portions ofsaid plate receiving the discharge for preventing deformation due tothermal distortion of said heat conducting means.

3. An electron discharge device, as defined in claim 2, furthercomprising energy conducting means at one end of the heat conductingmeans and extending away from the anode plate forming an energyconducting path.

4. An electron discharge device comprising an envelope, a cathode, aconductive gas within said envelope, an anode plate, heat-conductingmeans in contact with said plate for conducting heat away from saidplate comprising a plurality of paced, solid blocks, andenergyconducting means at one end of the heat-conducting means andextending away from the anode plate and forming an energy-conductingpath, said heat-conducting means comprising a support member with thesolid blocks mounted on one side of said member and the energyconductingmeans mounted on the other side of said member, a hollow cup memberhaving a flange extending from its edge, the outer edge of said flangebeing sealed to said envelope, said cup being rigidly connected to saidsupport member and forming a hollow shield fitting over said solidblocks, said anode plate being rigidly connected to said blocks, andenergy-conducting means extending through said hollow cup member,whereby an energy-conducting path is formed.

said energy conducting means further include tubulation 10 2,680,209

means extending therethrough.

6 9. An electron discharge device, as in claim 4, wherein said anodeplate is brazed to said blocks, said hollow cup member is brazed to saidsupport member, and the material of said braze is an alloy composed of82 percent gold and 18 percent nickel.

References Cited in the file of this patent UNITED STATES PATENTS2,621,303 Law Dec. 9, 1952 Veronda June 1, 1954 2,955,225 Sterzer Oct.4, 1960

